1. Field of the Invention
The present invention relates to a light intensity measuring apparatus for measuring a xenon excimer lamp that radiates a light beam having a central wavelength of 172 nm for a light intensity and an apparatus for detecting whether a xenon excimer lamp is on or off.
2. Related Art Statement
The tolerable level of contamination of semiconductor integrated circuits and liquid crystal substrates with organic compounds is becoming more severe with their finer processing. In their fabricating steps, therefore, techniques for optical cleaning or optical modification attract attention in recent years. In the optical cleaning or optical modification, a work is irradiated with a vacuum ultraviolet light beam for a predetermined period of time to cause a chemical reaction in an organic compound adhering to the surface thereof, whereby the surface is cleaned or modified.
As a light source for the above use, a xenon excimer lamp, particularly, a xenon excimer lamp having xenon sealed therein attracts attention, and introduction thereof into production lines has already started. The xenon excimer lamp having xenon sealed therein radiates a vacuum ultraviolet light beam, the light beam having a wavelength of 172 nm, and when the lamp is irradiated in an atmosphere containing oxygen, therefore, oxygen molecules (O2) absorb the light to generate active oxygen species such as oxygen atoms (O) and ozone (O3). Further, a light beam having a wavelength of 172 nm has a high photon energy of as high as approximately 7.2 eV, which is greater than bonding energies of most organic substances. When irradiation with the light beam having a wavelength of 172 nm is carried out, therefore, the chemical bonding of an organic compound can be broken, and the chemical compound can be efficiently removed by oxidation and decomposition thereof with generated active oxygen species.
When silicon wafers or liquid crystal substrates are cleaned or surface-modified with such a xenon excimer lamp, it is essential to measure a light beam radiated from the lamp for an intensity for finding performances thereof, and in an ultraviolet light beam irradiating apparatus having a xenon excimer lamp, it is required to confirm that the xenon excimer lamp is properly working, i.e., is on during the operation of the apparatus.
For measuring the above xenon excimer lamp for a light intensity or detecting on/off of the lamp, it is thinkable to use a light-sensing device having an optical sensitivity to the above light beam having a wavelength of 172 nm. As described above, however, the light beam having a wavelength of 172 nm has a relatively large photon energy, which causes a problem that a light-sensing device is therefore deteriorated to a great extent, and further, few devices have high productivity as such a device, which involves a problem that the cost of the device increases.
For the above reasons, conventionally, it is general practice to measure a xenon excimer lamp for a light intensity by the following method.
(a) A method in which the measurement is carried out with a photoelectric tube having sensitivity at 172 nm.
(b) A method in which a fluorescent material is irradiated with a light beam having a wavelength of 172 nm to convert the light to visible light, and the visible light is received in a light-sensing device sensitive to visible light such as a silicon photodiode, to measure the light intensity(e.g., JP-A-8-136339).
The former method of using a photoelectric tube has a problem that a supplementary apparatus is required so that the entire apparatus is increased in size and that the cost therefor increases. The latter method for the measurement with a combination of a fluorescent material and a photodiode has a problem that the fluorescent material is deteriorated by irradiation with the above ultraviolet light beam.
It is therefore an object of the present invention to provide a small-sized and less expensive light-intensity measuring apparatus and an on/off detecting apparatus for a xenon excimer lamp, which require no supplementary apparatus.
It is another object of the present invention to provide a light-intensity measuring apparatus and an on/off detecting apparatus for measuring a light beam having a wavelength of 172 nm for a light intensity with a device or part which is not much deteriorated with ultraviolet light beams.
The present invention is concerned with a light-intensity measuring apparatus for measuring a xenon excimer lamp that radiates a light beam having a central wavelength of 172 nm for a light intensity. The light-intensity measuring apparatus of the present invention has a characteristic feature in a constitution having a photoelectric converting device having a photosensitivity in a range of from 800 to 1,000 nm. Further, the light-intensity measuring apparatus of the present invention preferably comprises an operating means for relatively determining the intensity of a light beam having a central wavelength of 172 nm and a transmitting means for transmitting the light intensity determined with the above operating means.
The above operating means is preferably for relatively determining the intensity of the light beam having a central wavelength of 172 nm on the basis of a light-intensity integral value of spectrum of light in the range of from 800 to 1,000 nm.
In an experiment conducted by the present inventor, the intensity of the light beam at 172 nm emitted from a xenon excimer lamp and the total sum of light intensity of spectrum of light in the range of from 800 to 1,000 nm have a correlation as shown in a graph of FIG. 1. This result has clearly showed that the intensity of the light beam at 172 nm can be relatively determined on the basis of the total sum of light intensities of spectrum of light in the range of from 800 to 1,000 nm.
Preferably, the light-intensity measuring apparatus of the present invention further has an optical filter for shutting off the input of light having a wavelength of 800 nm or shorter into the above photoelectric converting device.
The present invention is further concerned with an on/off detecting apparatus for detecting whether the xenon excimer lamp that radiates a light beam having a central wavelength of 172 nm is on or off. The on/off detecting apparatus has a characteristic feature in a constitution comprising a photoelectric converting device having a sensitivity to light in the range of from 800 to 1,000 nm. Further, preferably, the on/off detecting apparatus of the present invention has a constitution having a comparator for comparing an output of the above photoelectric converting device with a predetermined reference value to determine whether the xenon excimer lamp is on or off and a transmitting means for transmitting an on- or off-state of the xenon excimer lamp on the basis of a result of the above comparator.
Preferably, the on/off detecting apparatus of the present invention also has an optical filter for shutting off the input of light having a wavelength of 800 nm or shorter into the above photoelectric converting device.
In the present invention, further, there may be employed a constitution in which the above light-intensity measuring apparatus or the above on/off detecting apparatus is incorporated into an ultraviolet light beam irradiating apparatus having a xenon excimer lamp.